I was never worried about how and where I would do my 20 mile run because things have a way of working out. I seriously doubt I'll be doing it this year, but here's some info for those of you still in running shape.
Running Fit (running shoe and gear store) is hosting a 20 mile run on September 25, which was my scheduled 20-mile day, as I imagine it is for everyone attempting Detroit this year. For a $10 donation they are hosting runners on Hines Drive in Livonia (I wonder if it will be flooded...?). The site claims it will be traffic free and aid stations will be available every 2 miles. The hydration is worth the donation alone.
Here's the link http://www.runningfit.com/index.php?option=com_content&task=view&id=236&Itemid=84